The dioecious form of Hydrilla is believed to originate from the Indian subcontinent, specifically the island of Sri Lanka, although random DNA analysis also indicates India’s southern mainland as a possible source location. The monoecious form is believed to have arrived on our shores from Korea.

Hydrilla can be found infesting freshwater lakes, ponds, rivers, impoundments and canals.

How Hydrilla spreads:

Fragmentation
Tubers
Turions
Aquarium trade
Hitchhiking on boats
Dredging spoils

Ecological Impacts:
Creates dense mats that block sunlight and displaces native species
Stratifies the water column, decreasing dissolved oxygen levels
Can cause bluegreen algae blooms, leading to Avian Vacuolar Myelinopathy (AVM), a disease that attacks the nervous system of American coots and bald eagles

Economic Impacts:
Decreases the value of waterfront properties
Decreases the weight and size of sportfish (limits the amount of open water and natural vegetation)
Impedes recreational activities including fishing, boating, and swimming, which hampers the tourism economy

Record the location of potential sightings with as much detail as possible (GPS coordinates when possible, or visual references to get us as close to the exact site as possible). Take a picture with as many parts of the plant as possible (tuber, turions, whorl of 5 leaves, serrated leaf margins). When possible, take a voucher specimen.

For more information, contact Clearwater’s Invasive Species Program Coordinator at (845) 265-8080 x7114 or email at epstein@clearwater.org.

Biological: Biological control insects as part of efforts to control Hydrilla have been attempted in Florida with mixed results. Leaf-mining flies from Australia and India and a tuber-feeding weevil from India have been used overseas. The insects released are not native to NY, nor are they currently permitted for release in the State. The use of non-native species to attempt to control another non-native species can be risky if the newly released species out-competes native insects, causing a new invasive species problem. The use of sterile grass carp has been used with some success in small lakes in the southern US but would be impractical in lakes the size of the Finger Lakes.insects as part of efforts to control Hydrilla have been attempted in Florida with mixed results. Leaf-mining flies from Australia and India and a tuber-feeding weevil from India have been used overseas. The insects released are not native to NY, nor are they currently permitted for release in the State. The use of non-native species to attempt to control another non-native species can be risky if the newly released species out-competes native insects, causing a new invasive species problem. The use of sterile grass carp has been used with some success in small lakes in the southern US but would be impractical in lakes the size of the Finger Lakes.

Mechanical: Power weed cutters mow underwater weeds below the water surface and gather them onto a conveyor. The harvesting process is expensive, costing over $1,000 per acre. Because of Hydrilla’s rapid growth, mechanical harvesting needs to be performed several times per growing season. Since the mowing and removal process cannot capture every single fragment of Hydrilla stem and leaf, water and wind currents moving away from the harvest area can easily carry these fragments to uninfested areas of a waterbody and result in new populations taking root.

Suction harvesting: of Hydrilla growth by divers using very strong vacuum hoses can be used to remove Hydrilla from confined areas. However, as with drawdowns, if the underground tubers are not removed by dredging following the suction harvesting, regrowth can take place from the tubers during the next growing season. Further, any fragments that might escape during vacuum activities can float away to root and start new infestations.

Control of Water Levels: Another method of dealing with Hydrilla infestations is the control of water levels. Temporary control of Hydrilla has been shown to result from large-scale, long-term water drawdowns. However, since new plants can grow from the buried tubers, regrowth can take place when water levels are allowed to return to normal. Drawdowns also can have negative environmental impacts on native plant species and on fish populations.

Chemical Control: Chemicals are easier to apply, but also costly. Herbicide spraying works best in small, enclosed bodies of water, and does not work at all in larger bodies the size of a Finger Lake, or in moving water such as a stream, river or canal. Herbicides can also have unintended impacts on native flora, as well. For those reasons, permits for chemical control of Hydrilla are difficult to obtain in New York.

The best most effective way to control Hydrilla is the prevention of new Hydrilla infestations.

Clearwater Hydrilla, Now Found in our Waters

Clearwater Avian Vacuolar Myelinopathy

NYSDEC Hydrilla Fact Sheet

New York Invasive Species